The present invention relates, in general, to integrated circuits and, more particularly, to integrated circuit metallization systems.
In the manufacture of semiconductor devices, a metallization system is typically formed on a semiconductor die to promote bonding of the semiconductor die to a ceramic or a metal structure such as a leadframe. Generally, the metallization systems are comprised of multiple layers of metal such as layers of chromium, nickel, and gold (CrNiAu), layers of titanium, platinum, and gold (TiPtAu), or layers of titanium, nickel, and gold (TiNiAu). The first layer is generally chromium or titanium because of their ability to bond to semiconductor substrates. In addition, the metal of the first layer serves to couple the second metal layers, e.g., Ni or Pt, to the semiconductor die. A gold protective layer is formed over the second metal layer.
An important use of the metallization system is for bonding the semiconductor die to a leadframe. One technique for accomplishing the bonding step is a solder re-flow process. Because the bonding step is accomplished using a solder re-flow process, the bonded semiconductor-leadframe structure must subsequently be maintained at a temperature lower than the bonding temperature. Otherwise, the semiconductor die will become separated from the leadframe. Thus, subsequent processing steps must be carried out at temperatures lower than the initial bonding temperature. If subsequent processing steps require temperatures higher than the temperature of the solder re-flow process, the integrity of the die attach bond may be compromised. A drawback of prior art metallization systems is that the temperature limit of the die attach bond is very close to or higher than the temperature of subsequent solder re-flow processes.
Accordingly, it would be advantageous to have a semiconductor metallization system having temperature limits that permit high temperature processing after formation of the metallization system. In addition, it would be advantageous to have a metallization system that inhibits dissolution of metals at bonding temperatures.